The present invention relates to devices for introducing perturbations into a flow field near a wing surface or other surface and, in particular, it concerns an active flaperon assembly for delaying or controlling boundary layer separation.
It has been found that mechanical energy (momentum) supplied in the form of perturbations of certain frequencies to the air flow passing over a wing helps to delay boundary layer separation from the surface of the wing, thereby increasing the lift, decreasing drag or otherwise improving the performance which can be obtained from the wing. This principle and various structures for implementing it are described in U.S. Pat. No. 5,209,438 to one of the co-inventors of the present invention. The aforementioned patent is hereby incorporated by reference as if fully set out herein.
While the principle described in the aforementioned patent has been demonstrated to be effective, to the best of the inventors' knowledge, no application of the principle has yet been widely implemented. This may be due to concerns as to the effect of the required wing modifications during normal flight when the perturbations are not required. While the aforementioned patent describes, on a highly schematic level, a number of possible structures for introducing the required perturbations, all of the structures modify existing wing designs to some extent and alter the basic wing profile.
Reference is also made to an unpublished U.S. patent application Ser. No. 09/045,220 to the other co-inventor of the present invention. This application addresses various piezoelectric materials and associated configurations suitable for generating perturbations in the air flow.
There is therefore a need for an active system for generating perturbations in the air flow over a wing which would require little or no modification of a conventional wing structure and which would not affect the air flow when not in use.